Measuring compressive loads on a ‘smart’ lumbar interbody fusion cage: Proof of concept

January 15, 2023

doi: 10.1016/j.jbiomech.2023.111440.

Online ahead of print.

Affiliations

¹ School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia; Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia. Electronic address: [email protected].
² Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, New South Wales, Australia.
³ School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia.
⁴ Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; Spine Service, Department of Orthopaedic Surgery St. George Hospital Campus, Kogarah, New South Wales, Australia.
⁵ School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia.

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Vivek A S Ramakrishna et al.

J Biomech.

2023.

doi: 10.1016/j.jbiomech.2023.111440.

Online ahead of print.

Affiliations

¹ School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia; Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia. Electronic address: [email protected].
² Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, New South Wales, Australia.
³ School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia.
⁴ Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; Spine Service, Department of Orthopaedic Surgery St. George Hospital Campus, Kogarah, New South Wales, Australia.
⁵ School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia.

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Abstract

There are several complications associated with lumbar interbody fusion surgery however, pseudarthrosis (non-union) presents a multifaceted challenge in the postoperative management of the patient. Rates of pseudarthrosis range from 3 to 20 % in patients with healthy bone and 20 to 30 % in patients with osteoporosis. The current methods in post-operative follow-up – radiographs and CT, have high false positive rates and poor agreement between them. The aim of this study was to develop and test a proof-of-concept load-sensing interbody cage that may be used to monitor fusion progression. Piezoresistive pressure sensors were calibrated and embedded within a polyether ether ketone (PEEK) interbody cage. Silicone and poly (methyl methacrylate) (PMMA) were inserted in the graft regions to simulate early and solid fusion. The load-sensing cage was subjected to distributed and eccentric compressive loads up to 900 N between synthetic lumbar vertebral bodies. Under maximum load, the anterior sensors recorded a 56-58 % reduction in pressure in the full fusion state compared to early fusion. Lateral regions measured a 36-37 % stress reduction while the central location reduced by 45 %. The two graft states were distinguishable by sensor-recorded pressure at lower loads. The sensors more effectively detected left and right eccentric loads compared to anterior and posterior. Further, the load-sensing cage was able to detect changes in endplate stiffness. The proof-of-concept ‘smart’ cage could detect differences in fusion state, endplate stiffness, and loading conditions in this in vitro experimental setup.

Keywords:

Instrumented implant; Interbody cage; Interbody fusion; Load sensing; Smart implant.

Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.